When lithium-ion batteries are configured to supply and store power from a vehicle they may be exposed to many charging and discharging cycles. For example, during a discharge cycle the battery may provide power to propel the vehicle, cool vehicle occupants, and provide entertainment. On the other hand, during a charging cycle the battery may be supplied power from a power supply or from vehicle wheels. However, if battery cells are charged more than a desired amount or discharged more than a desired amount the battery cells may degrade. Therefore, it may be desirable to accurately determine the state (e.g., voltage) of one or more battery cells so that battery charging or discharging may be limited during some conditions.
ADCs are one way to determine battery charge. In one example, the voltage of individual battery cells may be determined by selectively coupling individual battery cells to a higher resolution ADC (e.g., 12 bit resolution). If a particular battery cell is above a desired voltage, the particular battery cell can be discharged based on the ADC output. In this way, it is possible to determine and regulate charge of individual battery cells.
However, when only a single ADC is used to determine battery cell voltage, it may be more difficult to determine degradation of the battery cell voltage measurement. For example, if the ADC output drifts beyond an expected threshold amount, it may be difficult to determine that the ADC output is drifting. Further, it may be difficult to determine if there is degradation of circuitry between the battery cell and the ADC. For example, if switching circuitry between the ADC and battery cells does not switch in a desired manner, the ADC may read the same battery cell more times than is desired.
The inventor herein has developed a system for assessing ADC operation and voltage of a battery, comprising: a first ADC for determining the voltage of at least one battery cell; a second ADC for determining the voltage of a plurality of battery cells; and a controller performing an action in response to comparing an output of said first ADC to an output of said second ADC.
By comparing the output of one ADC to the output of another ADC, it may be possible to determine if circuitry or ADC output has degraded. In one embodiment, a first single higher resolution ADC may be selectively coupled to one or more battery cells. The first ADC output of the battery cell voltage may be stored to memory of a microcontroller during the time period that the first ADC is coupled to the battery cell. Once the first higher resolution ADC has stored the voltage of each battery cell of a battery cell stack to memory, a second lower resolution ADC may be coupled to the series combination of the same battery cells to determine the voltage of the plurality of battery cells. In particular, a microcontroller may then compare the sum of individual battery cell voltages as measured by the first higher resolution ADC to the battery cell voltage formed by the physical series combination of the same battery cells and as indicated by the second lower resolution ADC. Thus, the output of the first higher resolution ADC may be compared to the output of the second lower resolution ADC. If the output of one ADC is different from the output of the other ADC by more than a predetermined amount, the microcontroller may take an action. For example, if the output of one ADC is greater than the output of the other ADC by more than a predetermined amount, the battery pack may indicate that it is desirable to service the battery pack.
The present description may provide several advantages. For example, the approach may provide improved control over the state of charge of a battery pack because the battery pack may be operated closer to operational limits Further, the approach may provide improved battery cell diagnostics. Further still, the approach may provide alternative ways to operate the battery pack since the second ADC may still provide useful battery data even if operation of the first ADC has degraded. In addition, the approach may increase battery life as a higher percentage of the available battery capacity may be utilized.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.